Tools for the controlled tightening of bolts and other threaded objects are often provided with an indication of when the turning moment has reached a predetermined value and include a spring whose force can be adjusted to a value corresponding to the intended indication moment, for instance by displacement of one of the ends of the spring when rotating the grip of the tool. Thereafter, the tool can be used to tighten several bolts with the same turning moment.
For applications with particularly rigid safety regulations, for instance in aircraft industry, chemical or nuclear industry, there is a necessity to be able to adjust the spring force and the indication moment with a higher precision than what is normally possible with usual tools and to lock the tightening device of the spring so that the preset moment cannot change during work. The present invention relates to a tightening device for this purpose.